Related Products: SD Module Family(SD1, SD2, SD3, SD4, SD5), DS Module Family (DS1, DS2, DS3, DS4, DS5, DS6, DS7, DS8, DS9, DSN)
Connect Synchro / Resolver to NAI Card / Instrument
How do I connect my synchro / resolver to the NAI card or instrument? What is NAI Synchro / Resolver signal convention?
The NAI convention is as follows:
| NAI Connection | SYN Connection | RSL Connection |
|---|---|---|
| S1 | S1 | SIN(-) |
| S2 | S2 | COS(+) |
| S3 | S3 | SIN(+) |
| S4 | S4 | COS(-) |
What voltage relationships define this convention?
NAI synchro/resolver products follow the electromechanical conventions of MIL-S-20708 (synchros) and MIL-R-21530 (resolvers). Writing the rotor (reference) excitation as E(rotor) · sin ωt — where the excited rotor winding is R1−R2 for a synchro and R2−R4 for a resolver — the stator line-to-line voltages as a function of shaft angle θ are:
Synchro (MIL-S-20708) — three stator voltages, 120° apart, referenced to R1−R2:
| Line-to-line voltage | Equals |
|---|---|
| E(S3−S1) | N · E(R1−R2) · sin θ · sin ωt |
| E(S2−S3) | N · E(R1−R2) · sin (θ + 120°) · sin ωt |
| E(S1−S2) | N · E(R1−R2) · sin (θ + 240°) · sin ωt |
Resolver (MIL-R-21530) — two stator voltages in quadrature, referenced to the excited rotor winding R2 (HI) − R4 (LO):
| Line-to-line voltage | Equals |
|---|---|
| E(S3−S1) | N · E(R2−R4) · sin θ · sin ωt |
| E(S2−S4) | N · E(R2−R4) · cos θ · sin ωt |
Where:
- N is the transformation ratio of the transducer (stator L-L voltage at maximum coupling ÷ rotor voltage).
- θ is the shaft angle, positive for counter-clockwise rotation from electrical zero as viewed from the shaft end.
- sin ωt is the reference carrier; a positive coefficient means the stator voltage is in phase with the reference, a negative one means it is 180° out of phase.
These equations are the basis for the SIN/COS polarities in the table above: S3 is SIN(+) and S1 is SIN(−) because E(S3−S1) carries sin θ, and S2 is COS(+) and S4 is COS(−) because E(S2−S4) carries cos θ. At electrical zero (θ = 0°) the S3−S1 voltage is at null and the S2−S4 voltage is at maximum, in phase with the reference.
Note
MIL-R-21530 names the two resolver rotor windings R1−R3 and R2−R4, and the convention above assumes a transmitter excited on R2 (HI) / R4 (LO). NAI modules have a single reference pair per channel, labelled RHI / RLO (R1 / R2 in the getting-started guides) — connect the resolver’s excited rotor winding to it with HI to RHI and LO to RLO so that the signs come out as tabulated.